1. Field of the Invention.
This invention has relation to continuous flow grain dryers of the type wherein a column of grain to be dried and conditioned is formed between a pair of concentric, spaced-apart, pervious ring-like walls encircling a heater/blower assembly. This assembly heats and blows air into an upper plenum inside the inner wall. This hot air passes out through the pervious walls to heat and dry the grain, drawing cooling air into a lower plenum inside the inner wall and separated from the upper plenum by a baffle plate which surrounds the heater/blower assembly.
2. Description of the Prior Art.
It is conventional to utilize concentric, cylindrical pervious walls in grain column dryers which pass heated air outwardly through an upper plenum and which utilize cooling ambient air passing through the portion of the dryer horizontally aligned with a cooling plenum. Such structures are shown in U.S. Pat RE 25,230 to Pierpoint originally granted on Jul. 11, 1961; U.S. Pat. 3,440,734 to Batterton et al granted on Apr. 29, 1969; and U.S. Pat. 4,446,631 to Batterton et al, granted on May 8, 1984.
One effective way to accomplish this air flow is to suck the air in through a lower cooling section of concentric walls, to heat this air in the center of the dryer and then force the air out through the walls aligned with the heated plenum. See U.S. Pat. 2,654,590 to Molenaar, granted on Oct. 6, 1953; U.S. Pat. 3,233,337 to Tomlinson granted Feb. 1966; U.S. Pat. 3,333,348 to Ausherman et al granted on Aug. 1, 1967; U.S. Pat. 3,474,903 to Ausherman granted Oct. 28, 1969; and U.S. Pat. 3,896,562 to Zimmerman granted Jul. 29. 1975.
Grain dryers where a continuous flow of grain moves vertically as a grain column between two spaced-apart pervious walls and the heated drying air as well as the cooling air moves transversely through the grain column have been delineated generally as "crossflow grain dryers." In the middle 197O',s there was a switch from emphasis on performance of such high temperature grain dryers from improving dryer capacity to decreasing the energy consumption of the dryers. A paper on simulation results comparing the performance of three types of crossflow grain dryers was published and presented at the 1975 Annual Meeting of the American Society of Agricultural Engineers at the University of California-Davis, in Davis, California, June 22-25, 1975. The authors were Richard O. Pierce and Professor Thomas L. Thompson of the Agricultural Engineering Department of the University of Nebraska at Lincoln, Nebraska; and the paper was published by the American Society of Agricultural Engineers, St. Joseph, Michigan 49085. The title of the paper was Energy Utilization and Efficiency of Cross Flow Grain Dryers.
Of particular interest is FIG. 1 of this paper which presents a schematic diagram of the three crossflow dryer types studied. These three types are:
(a) "conventional crossflow dryer" typified by the patents cited above;
(b) "reversed crossflow dryer" in which, apparently, the upper portion of the grain column is dried by flow from one direction, say left to right through the vertically moving grain column, an intermediate section is dried by causing the hot air to flow in the opposite direction, say from right to left, and a bottom portion is subject to a crossflow from ambient air as a cooling stage; and
(c) a dryer where heated air from a mixing chamber is forced through an upper section of a grain column and out to the atmosphere, other heated air is forced through an intermediate section in one direction, say from left to right, and is then recirculated back into that same section to flow in the reverse direction, say from right to left, this reverse flow are then passing back into the mixing chamber together with a flow of ambient air which has first passed through a bottom, cooling section.
The Pierce/Thompson paper reported that definite economies in energy utilization could be obtained by some recirculation of the drying air back through the grain column in a manner similar to that shown in FIG. 1c. No suggestions were made as to configuration of dryers to accomplish these improved results, however.
Three patents of which the present inventor is aware each show structure which utilized an impervious structure in surrounding relation to concentric pervious walls that encompass a grain column. In this way, some measure of recirculation of heat energy components was apparently achieved. These include U.S. Pat. No. 4,289,481 granted to Yano on Sept. 15, 1981; U.S. Pat. No. 4,308,669 granted to Noyes et al on Jan. 5, 1982; and U.S. Pat. No. 4,337,584 granted to Johnson on Jul. 6, 1982.
In the Yano patent, however, all that was "reclaimed" was, apparently, the fines which blew out through the pervious walls. These were separated in a cyclone and/or filter screen separator and fed back into the burner where they were consumed to add to the heat energy.
In much of the prior art cited above, an impervious cone "capped" the inner pervious wall, and grain to be dried was delivered to the top of that cone where it s-id down to a position between the inner and outer pervious walls. Two patents disclose portable crossflow grain dryers utilizing pervious cones where the outward flow of heated, moisture-laden air is not only through the vertical grain dryer portions but also through grain resting on top of the pervious cone. These are U.S. Pat. No. RE 27,573 to Kucera, originally issued Aug. 18, 1970; and U.S. Pat. No. 4,118,875 granted to Sietmann et al, on Oct. 10, 1978. The structure of each of these patents requires that a layer of grain lies on top of the pervious cone. If no such grain were present, then the heated air would rise out of the top of the cone without a substantial drying effect on the grain in the grain column.
While the Sietmann et al '875 patent shows a layer of grain lying on top of the pervious cone 18, neither that patent nor the Kucera patent suggests how that layer can be achieved and how it can be maintained at a level to permit uniform control over the drying process. In each patent it is apparently contemplated that grain will be added at a rate sufficient to keep most of the side board extending above the outer pervious wall pretty well filled to the top with grain so that the layer on top of the pervious cone is at all points at least as thick as the grain column itself.
An earlier patent to Sietmann, U.S. Pat. No. 3,479,748, granted on Nov. 25, 1969, discloses a batch grain dryer in which an "overhead floor structure indicated generally at 37 in FIG. 1" includes a pervious cone on which the batch of grain to be dried is directed, and a "drying apparatus indicated generally at 41 in FIG. 2". See Sietmann et al '748, paragraph beginning on column 3, line 51. This drying apparatus consists of a blower/heater 92 connected to an opening 91 just below the "overhead floor structure 37" and high up on a pervious cylindrical wall or side wall 13. See column 5, beginning on line 36 and FIGS. 2 and 1. Additionally, for introducing ambient air, "A blower system (not shown) is fluidly communicable with the trough 18 through a duct 22, and upon energizing the blower, air is forced into the trough 18 whereby it percolates upwardly up through the perforated floor plate 19 and through granular material stored thereon for aeration purposes." See column 3, beginning on line 24.
A series of cylindrical "upper bands 73, 74 and 76" and "lower bands 96, 97 and 98" are provided with adjustments "such that any particular amount of grain which is desirable to be dried at one time above the floor 42 can be so handled by this apparatus." Paragraph beginning on column 7, line 9.
This "raised floor" or "overhead floor structure" includes "a plurality of particularly placed openings formed therein, closed by a remote operator-controlled device whereby the grain, after drying, can be dumped in an even, level manner onto the base floor" See column 1, beginning on line 19.
From a consideration of the Sietman '748 patent and the above summary of it, it is evident that the grain is in a static position while it is being heated and dried by a relatively general upward flow of heated air introduced at a side of and beneath the "raised floor" or "overhead floor structure" After it has been dried, it "can be dumped in an even, level manner onto the base floor" while it is still hot and allowed to lie there on top of a "perforated plate 19 capable of holding granular material while enabling air from there below to pass upwardly therethrough." "A blower system (not shown) is fluidly communicable with trough 18 through duct 22, and upon energizing the blower, [cool, ambient]air is forced into the trough 18 whereupon it percolates upwardly through the perforated floor plate 19 and through granular materials stored thereon for aeration purposes." Column 3, lines 17 through 29. This upward flow of cooling air through static, hot, dried grain which lies evenly on the plate 19 is not part of the drying process, and one can presume that it is being carried out while the "raised floor" is being reloaded with the next batch of grain to be dried. No recycling of either the cooling air after it has passed through the grain lying on plate 19 nor of the heating air passing from the blower/heater 92 and out through the top of the pervious cone is contemplated, and all energy expended heating and blowing the drying air and the cooling air is lost as the air passes out of the top of the dryer.
The inventor and those in privity with him are aware of no prior art closer than that discussed above and are aware of no prior art which anticipates the claims set out herein.